In the past few years low emissivity and reflective windows have been introduced to the market and have become very popular. Low emissivity windows are popular because they can reduce the heating and cooling costs of buildings by reflecting most of the infrared radiation while allowing in most of the visible radiation. Reflective windows also reduce heating costs by reflecting unwanted radiation. Also in the past few years architects have been designing buildings with curved panes of glass and it would be advantageous to have this glass coated with a low emissivity coating. There are also other needs for curved low emissivity and reflective glass panes which can be bent or shaped as specified such as for use in cars.
Most curved glass cannot fit through or be evenly coated in a sputtering machine due to the degree of arc in the curve of the glass. Therefore a flat piece of glass needs to be bent to the desired shape after the coating has been applied. Unfortunately, to bend a piece of glass it has to be heated to be shaped and this heating and bending will ruin most coatings.
If a slightly bent piece of glass can fit into and be coated in a sputtering machine there is a high rate of breakage in the cleaning process following the coating, therefore it is advantageous to sputter a flat piece of glass and then bend it.
Currently the only method known to the applicant of providing temperable low emissivity coatings on glass such that the glass may be heated and shaped is by using a glass substrate coated with a first layer of tin oxide, a second layer of aluminum, a third layer of silver, a fourth layer of aluminum and a fifth layer of tin oxide. Then the glass is heated to shape it.
One disadvantage of this method is that the heat levels must be carefully controlled. When heated, the aluminum layers will absorb oxygen, forming aluminum oxide layers. If the temperature gets too high the silver layer will also oxidize, ruining the visibility though the coating.
Another disadvantage of the above method is that sputtering aluminum is a difficult procedure. Since aluminum is a good conductor it arcs during sputtering, and it is not a clean material to sputter.
There are sputtering machines such as Airco Solar Product's coater on the market for sputtering layers of metals on a substrate. Airco's machine has 5 separate chambers having 3 cathodes in each chamber. Each cathode may be a different metal and the atmospheres in each chamber may be a different gas at a different pressure. Each cathode may be energized at a different voltage and the speed of the glass in the chambers may be varied to increase or decrease the thickness of the layers of metal deposited on the substrate.
Once the cathodes are in place it requires about 2 days of down time to change the cathodes. Because of this down time it is important to be able to make several products without having to change the cathodes.
It is therefore commercially important to make a large variety of products without having to change the cathodes. Switching cathodes within the machine can be done by shutting off or turning on one or more of the 15 cathodes in the 5 chambers. It is easy to change the atmosphere of a chamber. A wide variety of combinations can then be selected without causing expensive down time.
Applicant has been manufacturing Regular Low Emissivity glass by using this type of sputtering machine in which the first chamber has an oxygen atmosphere and the 3 cathodes are first zinc, second tin, and third zinc. The substrate is then coated with a zinc tin oxide mixture. In the second chamber the cathodes are first titanium, second silver, and third titanium. This chamber has an argon atmosphere, which is an inert gas to promote the layers being pure titanium and silver. Only the second and third cathodes are turned on in this chamber to provide a layer of silver and a layer of titanium. The third chamber has a first cathode of tin, a second cathode of zinc and a third cathode of tin, in an oxygen atmosphere. This produces a tin zinc oxide mixture layer. The fourth chamber has a first cathode of stainless steel, a second cathode of titanium, and a third cathode of titanium. Only the titanium cathodes are turned on in this chamber. The atmosphere in this chamber is oxygen which produces a titanium oxide layer. The fifth chamber has all three cathodes of titanium in an oxygen atmosphere. This produces a titanium oxide layer.
For another product, the Sun Low Emissivity window, all the cathodes are the same but the last two chambers have a nitrogen atmosphere instead of an oxygen atmosphere. This produces a titanium nitride for the outer layers instead of a titanium oxide.
Another product made on this machine is a high performance insulating reflective glass using the stainless steel of chamber four, cathode one, in an argon atmosphere for the first layer coated on a glass substrate and having a second layer of titanium using all three cathodes of titanium in the fifth chamber in a nitrogen atmosphere for a titanium nitride layer.
Another product uses all the titanium cathodes in a nitrogen atmosphere to give a titanium coating.
Many other combinations of coatings are possible.
In order to manufacture bendable low emissivity coatings on glass by the known method the sputtering machine would have to be shut down to change the cathodes in chamber 2 from aluminum to titanium, causing down time and lost production.
The inventor has developed a coating that will not be damaged in the heating and shaping process using a layer of titanium on each side of a layer of silver.
Using titanium has several advantages.
First, there is no down time to change cathodes in the sputtering machine.
Second, titanium will not absorb oxygen as easily as aluminum when heated and therefore will protect the silver from oxidizing better during the heating and shaping process, thus reducing the rejection rate.
Third, titanium is easier to sputter. It does not have the arcing problems of aluminum, it sputters more cleanly and therefore requires less cleaning.
Fourth, Titanium is a harder, more scratch resistant material than aluminum.
Fifth, titanium is slightly more transparent to visible light than aluminum.
And sixth, titanium oxide aesthetically looks better than aluminum.
Using the same machine and cathodes with a split cathode having silver and stainless steel for the silver cathode a temperable reflective glass can be produced.